1. Field of the Invention
The present invention relates to a photodiode built-in semiconductor device for light signal reception. The device can prevent an erroneous operation in accordance with unnecessary incident light.
2. Description of the Related Art
Semiconductor devices which include a light receiving photodiode and its peripheral circuits have been used on the receiving side of various light signal transmission systems. For example, in an infrared-ray signal transmission system, or in light pick-up devices of laser-signal readers, such semiconductor devices including a photodiode and its peripheral circuits are utilized. There are two kinds of photodiode built-in semiconductor devices. One is a monolithically integrated semiconductor device on a silicon substrate, and the other is a hybrid-integrated device arranging discrete devices on a ceramics substrate. Monolithically integrated devices can lower costs in manufacture compared with hybrid type devices, and are immune to external electromagnetic noises. Therefore monolithically integrated semiconductor devices are the subject matter of the present invention.
Since a photodiode, its peripheral NPN transistors, and so on coexist in a photodiode built-in semiconductor device, it is necessary to block incident light other than the photodiode in order not to generate light currents in the peripheral circuits depending on unnecessary light injections.
The simple and easy method for blocking light injections to peripheral circuits is to cover the peripheral circuits regions with a top aluminum metallization film (or wiring layer) by using one of multilayer metallizations for semiconductor integrated circuit devices. However, bonding pads which are arranged on the semiconductor device to connect the internal circuits to external circuits with a wire must be formed on the chip by using at least one of multilayer metallizations. Hence a space is formed between the bonding pads and the light shielding film on the periphery circuits. Therefore unnecessary light injects in to the periphery circuits through the space, and causes undesired light current generation in the periphery circuits.
The inventors of the present invention already proposed a structure of a photodiode built-in semiconductor device that can block light injection from the space between the bonding pads and the light shielding film with Japanese Patent Application No. (Heisei) 4-287582.
FIGS. 4 through 6 show the structure of the above-mentioned photodiode built-in semiconductor device. In these figures, numeral 10 represents a bonding pad; numeral 11 represents an extension region of the bonding pad; numeral 12 represents a light shielding film; and numeral 13 represents a second light shielding film. As shown in FIG. 5, the bonding pad 10 is formed by laminating sequentially the first, second, and third aluminum metallizations (or wiring layers) 14, 15, and 16. The extension region 11 of the bonding pad 10 is formed so as to expand outward the second aluminum metallization 15, other than the metallizations 14 and 16. The second light shielding film 13 is disposed between the metallizations 14 and 14 of the bonding pads 10 and 10, with the extension region 11 overlapped with the film 13. A second interlayer insulating film 17 insulates the expanding bonding pad region 11 from the second light shielding portion 13. Similarly, the light shielding film 12 formed of the third aluminum metallization 16 is arranged so as to overlap with the extension portion 11 of the second metallization 15 of the bonding pad 10. The light shielding film 12 is insulated from the extension portion 11 by the second interlayer insulating film 18. As stated above, utilizing multilayer metallizations and multilayer insulations, the top surface of the silicon substrate is entirely covered with aluminum metallizations overlapped with each other, except for an exposure surface of the photodiode.
The above-mentioned structure is very effective with the light injected perpendicularly to the top surface of the chip, but is defenseless to the light injected slantingly, or not perpendicularly to the top surface of the chip. In other words, the light shielding films 12 and 13 do not have any light shielding effect as to the light 19 injected perpendicular to the side surface (diced cut surface) of the chip. As a result, if there is light which is injected in a direction that is not perpendicular to the top surface of the photodiode built-in semiconductor chip, then it generates photocurrent at the PN junctions of the periphery circuits of the semiconductor device, causing erroneous operation. Since the dicing step inevitably follows after a completion of the wafer process, it is technically impossible to form the light shielding film on the side surface of the photodiode built-in semiconductor chip.